Level 6 Mastery token/reaching level 5

I'm not sure if it's a bug or just an unintended notification, but upon reaching level 5 with a certain champion while simultaneously earning an S in the same game, the "you have earned a mastery token" notification pops up. But when I went to check my tokens to level up the champ, it wasn't there. Its happened twice to me now, one for Quinn and one for Malzahar. I earned an S rank while simultaneously reaching level 5, got the token notification, but no token after.